Charles Eugene Flandrau (July 15, 1828 – September 9, 1903) was an American lawyer who served on the Minnesota Supreme Court. He was also a colonel in the Union Army.
Flandrau was born in 1828 in New York City. His father was Thomas Hunt Flandrau of New Rochelle, New York, a law partner of Aaron Burr. His mother was Elizabeth Maria Macomb, a daughter of Alexander Macomb, the wealthy New York merchant, and half-sister of General Alexander Macomb, hero of the War of 1812 and afterward head of the United States Army. The Flandraus were descendants of Jacques Flandreau, a Huguenot who came to New Rochelle in the 1690s.
Flandrau was educated in Georgetown, then a separate community in the District of Columbia, until the age of 13 when he tried to enlist in the Navy. Too young to obtain an appointment, he instead spent three years as a common sailor under other services. In 1844, tiring of the sea, he spent three years in the mahogany trade in New York City, after which he rejoined his family at Whitesboro, New York, where he apprenticed in his father's law practice. He passed the bar in 1851 and joined his father's firm as partner.
In 1853, he relocated to Traverse des Sioux, Minnesota to practice law. During the 1850s, he served on the Minnesota Territorial Council, in the Minnesota Constitutional Convention, and on the Minnesota territorial and state supreme courts. He was also appointed U.S. Agent for the Sioux in 1856.
In August 1862, learning of a violent Dakota uprising in the southwestern corner of the state, he enlisted in the Union Army as a captain, and assembled an armed force to rush to the defense of the community of New Ulm. It is in honor of his success there that both Flandrau State Park and the community of Flandreau, South Dakota, are so named. Governor Ramsey put him in charge of the defense of the southwestern frontier of the state, and he served in this capacity as colonel for two years, simultaneous to his position on the Minnesota Supreme Court.